Dissolving-Grade Pulp Compositions

ABSTRACT

Dissolving-grade pulp compositions are prepared by treating a cellulosic material with an extractant comprising a cellulose solvent and co-solvent. The dissolving-grade pulp compositions comprise at least 90 wt. % glucan, from 0.6 to 5 wt. % xylan, and have distinct molecular weights, and elemental metal ions from known and commercially available dissolving-grade pulp compositions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional App. No. 61/941,938, filed Feb. 19, 2014, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to dissolving-grade pulp compositions and to processes for producing dissolving-grade pulp compositions. In particular, the present invention relates to dissolving-grade pulp compositions comprising at least 90 wt. % glucan and from 0.6 to 5 wt. % xylan.

BACKGROUND OF THE INVENTION

Dissolving-grade pulp, also referred to as dissolving-grade cellulose, is a bleached wood pulp or cotton linter that has a high cellulose content, e.g., at least 90%. Dissolving-grade cellulose is characterized by a high α-cellulose content, i.e., it is composed of long-chain molecules, relatively free from lignin and hemicelluloses, and other short-chain carbohydrates. Dissolving-grade pulp may be further categorized into pulp grades of varying levels of purity, brightness, and viscosity suitable for the manufacture of cellulose esters (cellulose acetate, cellulose butyrate, cellulose propionate), nitrates, ethers, viscose, and microcrystalline cellulose.

Dissolving-grade pulps, and in particular high purity dissolving-grade pulps such as acetate-grade cellulose pulps, are useful in forming various cellulose derivatives For example, cellulose acetate is the acetate ester of cellulose and is used for a variety of products, including textiles (e.g., linings, blouses, dresses, wedding and party attire, home furnishings, draperies, upholstery and slip covers), industrial uses (e.g., cigarette and other filters for tobacco products, and ink reservoirs for fiber tip pens, decking lumber), high absorbency products (e.g., diapers, sanitary napkins, and surgical products), thermoplastic products (e.g., film applications, plastic instruments, and tape), cosmetic and pharmaceutical (extended capsule/tablet release agents and encapsulating agent), medicinal (hypoallergenic surgical products) and others.

High purity α-cellulose is commonly required as a starting material to make many cellulose derivatives, such as cellulose acetate. Acetate-grade pulps are specialty raw materials produced in commercial pulp processes, but the cost for such pulps is high. Commercial paper grade pulps contain less than 90% α-cellulose and are potential crude cellulosic sources for making cellulose derivatives. Paper grade pulp contains a high amount of impurities, such as hemicellulose, rendering it incompatible with certain industrial uses, such as making cellulose acetate flake or tow.

Zhou et al. discusses the use of dimethyldioxirane (DMDO), a pulp bleaching agent, to treat birch pulp and obtain acetate-grade pulp. However, currently, DMDO is not commercially available due to its instability. Therefore, it is not an ideal solvent for producing large quantities of high α-cellulose content pulp. Zhou et al. “Acetate-grade pulp from birch,” BioResources, (2010), 5(3), 1779-1778.

Studies have been done regarding the treatment of biomass to form biofuels. Specifically, it is known that various ionic liquids can be used to dissolve cellulosic material. S. Zhu et al. in Green Chem. 2006, 8, pp. 325-327, describe the possibility of dissolving cellulose in ionic liquids and recovering it by addition of suitable precipitating agents such as water, ethanol, or acetone.

Others have used ionic liquids to break down the cellulosic materials to make biofuels by way of glucose. For example, U.S. Pub. No. 2010/0112646 discloses a process for preparing glucose from a cellulose material, in which a cellulose-comprising starting material is provided and treated with a liquid treatment medium comprising an ionic liquid and an enzyme. Similarly, U.S. Pub. No. 2010/0081798 discloses a process for preparing glucose from a material containing ligno-cellulose, in which the material is first treated with an ionic liquid and then subjected to enzymatic hydrolysis. U.S. Pub. No. 2010/0081798 describes obtaining glucose by treating a material containing ligno-cellulose with an ionic liquid and subjecting same to an enzymatic hydrolysis and fermentation. However, in order to turn cellulose containing materials into glucose, the methods disclosed in these references result in breaking down the cellulose molecules, making them unsuitable for use as starting materials to make cellulose derivatives.

U.S. Pat. No. 7,828,936 describes a method for dissolving cellulose in which the cellulose based raw material is admixed with a mixture of a dipolar aprotic intercrystalline swelling agent and an ionic liquid. This method results in the complete dissolution of the cellulose and destruction of the fiber morphology of the cellulose. Although the cellulose may be regenerated using a non-solvent, the crystallinity of the regenerated cellulose is lower than the original cellulose sample.

The need exists for processes for producing dissolving-grade pulp from lower grade starting materials without destroying the fiber morphology and other characteristics of the cellulose structure. In particular, the need exists for dissolving-grade pulp compositions comprising at least 90% glucan and from 0.6 to 5 wt. % xylan and for cost effective methods for producing such compositions.

SUMMARY OF THE INVENTION

In a first embodiment, the invention is directed to a dissolving-grade pulp composition comprising at least 90 wt. % glucan and from 0.6 to 5 wt. % xylan, wherein the composition has a weight-average molecular weight of at least 500,000 g/mol. In some aspects, the composition may be a hardwood dissolving-grade pulp. In other aspects, the composition may be a softwood dissolving-grade pulp. The composition may comprise from 1 to 2 wt. % mannan. The composition may comprise arabinan and galactan. The composition may have a weight-average molecular weight from 500,000 to 3,000,000 g/mol. The composition may have a number-average molecular weight from 150,000 to 600,000 g/mol or from 175,000 to 450,000 g/mol. The composition may have a Z-average molecular weight from 900,000 to 50,000,000 g/mol. The composition may comprise less than 175 ppm sodium or less than 25 ppm sodium. The composition may comprise less than 7 ppm silicon. The composition may comprise less than 10 ppm potassium. The composition may comprise less than 0.01 wt. % dichloromethane extractables. In some aspects, the composition may have a weight ratio of xylan to mannan from 1:1 to 3:1. In other aspects, the weight ratio of xylan to mannan is less than 1:2.

In a second embodiment, the invention is directed to a dissolving-grade pulp composition comprising at least 90 wt. % glucan and from 0.6 to 5 wt. % xylan, wherein the composition comprises less than 175 ppm sodium. In some aspects, the composition is a hardwood dissolving-grade pulp. In other aspects, the composition is a softwood dissolving-grade pulp. The composition may comprise from 1.1 to 5 wt. % mannan. The composition may have a weight-average molecular weight of at least 500,000 g/mol, or from 500,000 to 3,000,000 g/mol. The composition may comprise less than 25 ppm sodium. The composition may comprise less than 7 ppm silicon. The composition may comprise less than 10 ppm potassium.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be better understood in view of the appended non-limiting figures, in which:

FIG. 1 shows an exemplary purification process in accordance with one embodiment of the present invention;

FIG. 2 shows an exemplary purification process in accordance with another embodiment of the present invention; and

FIG. 3 shows an exemplary purification process in accordance with yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION I. Introduction

The present invention relates to dissolving-grade pulp compositions and to processes for producing dissolving-grade pulp compositions. The dissolving-grade pulp compositions comprise at least 90 wt. % glucan and from 0.6 to 5 wt. % xylan. Further, the dissolving-grade pulp compositions of the present invention preferably have distinct molecular weights and elemental metal ion contents which are different from commercially available dissolving-grade pulp compositions.

In one embodiment, the dissolving-grade pulp composition comprises at least 90 wt. % glucan, from 0.6 to 5 wt. % xylan, and has a weight-average molecular weight of at least 500,000 g/mol.

In some other embodiments, the dissolving-grade pulp composition may comprise at least 90 wt. % glucan, from 0.6 to 5 wt. % xylan, and less than 175 ppm sodium.

The present invention also relates to processes for producing dissolving-grade pulp compositions. In one aspect, the invention is to a process comprising separating, e.g., extracting, hemicellulose and other cellulosic impurities (e.g., dichloromethane (DCM) extractables and degraded cellulose) from a cellulosic material with an extractant to form an intermediate cellulosic material having a reduced hemicellulose content; and concentrating the intermediate cellulosic material to form a concentrated cellulosic material having an increased solids content. The extractant used in the separating step comprises a cellulose solvent and a cellulose co-solvent. The cellulose solvent should be suitable for dissolving hemicellulose, and preferably degraded cellulose and other impurities in the cellulosic material, and in combination with a co-solvent, should have little solubility for α-cellulose. The cellulose solvent is preferably selected from the group consisting of an ionic liquid, an amine oxide and combinations thereof, and the cellulose co-solvent is preferably selected from the group consisting of dimethyl sulfoxide (“DMSO”), tetramethylene sulfone, tetramethylene sulfoxide, N-methyl pyrrolidone, dimethyl formamide (“DMF”), acetonitrile, acetic acid, water, and mixtures thereof. The concentrated cellulosic material may be dried to form a finished cellulosic product, preferably a dissolving-grade pulp.

The processes of the invention are particularly suitable for separating and removing impurities, such as hemicellulose and/or degraded cellulose, from a cellulosic material to form a dissolving-grade pulp, the purity of which may vary somewhat depending largely on the composition of the starting cellulosic material, the composition of the extractant used, and extraction conditions. In preferred aspects, the finished cellulosic product comprises at least 90 wt. % cellulose and may be referred to as a dissolving-grade pulp.

II. Dissolving-Grade Pulp Compositions

As described herein, the present invention relates to dissolving-grade pulp compositions that comprise at least 90 wt. % glucan and from 0.6 to 5 wt. % xylan, based on a dried sample weight. As used herein, glucan refers to β-glucan. β-Glucans (beta-glucans) are polysaccharides of D-glucose monomers linked by β-glycosidic bonds. Cellulose is glucan with beta(1,4)-linkage. In terms of ranges, the dissolving-grade pulp composition may comprise 90 to 98.3 wt. % glucan, e.g., from 92 to 98 wt. %, or from 93 to 98 wt. % glucan and from 0.6 to 5 wt. % xylan, e.g., from 0.9 to 5 wt. %, from 1.7 to 4 wt. %, or from 1.9 to 3.5 wt. %. In some aspects, the xylan content may vary depending on whether the dissolving-grade pulp is a hardwood dissolving-grade pulp or a softwood dissolving-grade pulp. The softwood dissolving-grade pulp my comprise from 0.6 to 5 wt. % xylan while the hardwood dissolving-grade pulp may comprise from 1.7 to 5 wt. % xylan.

The dissolving-grade pulp compositions may further comprise arabinan, galactan, and mannan, generally in amounts totaling less than 20 wt. %, e.g., less than 10 wt. % or less than 5 wt. %. The dissolving-grade pulp compositions may comprise less than 0.2 wt. % arabinan, e.g., less than 0.1 wt. %, or less than 0.05 wt. %. In terms of ranges, the dissolving-grade pulp compositions may comprise from 0.01 to 0.2 wt. % arabinan, e.g., from 0.01 to 0.1 wt. % or from 0.01 to 0.05 wt. %. The dissolving-grade pulp compositions may comprise less than 0.2 wt. % galactan, e.g., less than 0.1 wt. %, or less than 0.05 wt. %. In terms of ranges, the dissolving-grade pulp compositions may comprise from 0.01 to 0.2 wt. % galactan, e.g., from 0.01 to 0.1 wt. % or from 0.01 to 0.05 wt. %. The dissolving-grade pulp compositions may comprise less than 5 wt. % mannan, e.g., less than 3 wt. % or less than 1.5 wt. %. In terms of ranges, the hemicellulose compositions may comprise from 0.01 to 5 wt. % mannan, e.g., from 1.1 to 5 wt. %, or from 1.1 to 2 wt. %. By using the processes described herein to form the dissolving-grade pulp, xylan is selectively removed in a greater amount than mannan. The selective removal of xylan may allow for fewer downstream processing steps for the dissolving-grade pulp, e.g., bleaching.

In some embodiments, the dissolving-grade pulp may be derived from hardwood and may have a weight ratio of xylan to mannan is from 1:1 to 3:1, e.g., from 1.5:1 to 3:1 or from 2:1 to 3:1. In some preferred aspects, the xylan is present in a larger weight amount than mannan. In further embodiments, the dissolving-grade pulp may be derived from softwood and may have a weight ratio of xylan to mannan of less than 1:2, e.g. less than 1:3, or less than 1:5.

Although weight percents of the polysaccharides in the dissolving-grade pulp compositions are reported, i.e., xylan, arabinan, galactan, glucan and mannan, these weight percents may be readily converted to corresponding monosaccharide content. For example, the xylan content in the sample may be calculated from the xylose content of carbohydrate analysis by multiplying by a factor of 0.88, and glucan or mannan by multiplying by a factor of 0.9.

The dissolving-grade pulp compositions may have increased molecular weights as compared to the cellulosic material from which they were derived. Without being bound by theory, the use of a cellulose solvent results in the selected dissolution of hemicellulose and other impurities which reduce or substantially eliminate cellulose dissolution. Thus, the dissolving-grade pulp may have a weight-average molecular weight higher than the starting cellulosic material, e.g., at least 10% greater, at least 20% greater or at least 30% greater. In some aspects, the dissolving-grade pulp compositions may have a weight-average molecular weight of at least 500,000 g/mol, e.g., at least 600,000 g/mol, at least 700,000 g/mol, or at least 750,000 g/mol. In terms of ranges, the dissolving-grade pulp may have a weight-average molecular weight from 500,000 to 3,000,000 g/mol, e.g., from 600,000 to 3,000,000 g/mol, e.g., from 700,000 to 3,000,000 g/mol or from 750,000 to 3,000,000 g/mol. The dissolving-grade pulp compositions may have a number-average molecular weight from 150,000 to 600,000 g/mol, e.g., from 175,000 to 450,000 g/mol or from 250,000 to 450,000 g/mol. The dissolving-grade pulp compositions may have a Z-average molecular weight from 900,000 to 50,000,000 g/mol, e.g., from 1,250,000 to 50,000,000 g/mol, or from 1,500,000 to 50,000,000 g/mol. The dissolving-grade pulp compositions may have a peak molecular weight from 400,000 to 2,000,000 g/mol, e.g., from 500,000 to 2,000,000 g/mol or from 600,000 to 2,000,000 g/mol. The polydispersity index of the dissolving-grade pulp compositions, calculated by dividing the weight-average molecular weight by the number-average molecular weight, may range from 1 to 5, e.g., from 1.5 to 5 or from 2 to 5.

Elemental metals and non-metals may be present in the hemicellulose compositions, including but not limited to silver, tin, bismuth, aluminum, arsenic, boron, barium, beryllium, cadmium, calcium, cobalt, chromium, copper, iron, potassium, magnesium, manganese, molybdenum, sodium, nickel, phosphorous, lead, sulfur, antimony, selenium, silicon, titanium, thallium, vanadium, and zinc. The presence and level of the above listed elemental metals and non-metals may be controlled by the dissolving-grade pulp preparation method. In particular, calcium content may be influenced by washing agents and sodium content may be influenced by the preparation process. In some aspects, the dissolving-grade pulp compositions may comprise less than 175 ppm Group IA metals, e.g., less than 100 ppm Group IA metals, less than 50 ppm Group IA metals or less than 25 ppm Group IA metals. In some aspects, the dissolving-grade pulp compositions may comprise less than 175 ppm sodium, e.g., less than 100 ppm sodium, less than 50 ppm sodium or less than 25 ppm sodium. In further aspects, the dissolving-grade pulp compositions may comprise less than 10 ppm potassium, e.g., less than 7 ppm potassium or less than 5 ppm potassium. In still further aspects, the dissolving-grade pulp compositions may comprise less than 7 ppm silicon, e.g., less than 5 ppm or less than 3 ppm. Without being bound by theory, by producing a dissolving-grade pulp having low silicon content, the hardness of the pulp may be improved, relative to dissolving-grade pulps comprising higher amounts of silicon. In some aspects, the total amount of elemental metals and non-metals disclosed above may be present at less than 1 wt. %, e.g., less than 0.5 wt. %, or less than 0.2 wt. % (2,000 ppm). In terms of ranges, the total amount of elemental metals and non-metals disclosed above may range from 100 ppm to 10,000 ppm, e.g. from 100 ppm to 5,000 ppm or from 100 ppm to 2,000 ppm. As used herein, parts per million (ppm) are determined on a weight basis.

III. Cellulosic Material

The dissolving-grade pulp compositions of the present invention may be formed from natural cellulosic materials, including plant and plant-derived materials. As used herein, the term “cellulosic material” refers to any material comprising cellulose, such as a pulp, and which may contain, for example, α-cellulose, hemicellulose and degraded cellulose. In preferred embodiments, the cellulosic material comprises wood pulp, e.g., paper grade wood pulp. When the cellulosic material is paper grade wood pulp, the processes described herein may be advantageously used to produce hemicellulose compositions and also to produce cellulose compositions, although the processes of the invention are not limited to the use of paper grade wood pulp as the starting cellulosic material.

In some embodiments, the cellulosic material may comprise a cellulosic raw material, which may include, without limitation, plant derived biomass, corn stover, sugar cane stalk, bagasse and cane residues, rice and wheat straw, agricultural grasses, hard wood, hardwood pulp, soft wood, softwood pulp, herbs, recycled paper, waste paper, wood chips, pulp and paper wastes, waste wood, thinned wood, cornstalk, chaff, and other forms of wood, bamboo, soyhull, bast fibers, such as kenaf, hemp, jute and flax, agricultural residual products, agricultural wastes, excretions of livestock, microbial, algal cellulose, and all other materials proximately or ultimately derived from plants. Such cellulosic raw materials are preferably processed in pellet, chip, clip, sheet, attritioned fiber, powder form, or other form rendering them suitable for extraction with the extractant. In some exemplary embodiments, the hemicellulose compositions are derived from hard wood pulps.

Generally, cellulosic material may be derived from lignin-containing materials, where lignin has been removed therefrom. In cellulosic materials, hemicellulose is linked to cellulose by hydrogen bonds. Overall, the cellulose material has a linear shape of fiber morphology, which is surrounded by hemicellulose via hydrogen bonds. These bonds between cellulose and hemicellulose may become weakened by treating the cellulosic material with an extractant to selectively dissolve the hemicellulose while maintaining the fiber morphology of the cellulose material, e.g., leaving the fiber morphology unchanged.

In one embodiment of the invention, the cellulosic material is a paper grade pulp provided in a form such as, but not limited to, a roll, a sheet, or a bale. Preferably, the paper grade pulp comprises at least 70 wt. % α-cellulose, e.g., at least 75 wt. % α-cellulose or at least 80 wt. % α-cellulose. Paper grade pulp typically also comprises at least 15 wt. % hemicellulose, at least 20 wt. % hemicellulose or at least 25 wt. % hemicellulose. In another embodiment, the cellulosic material may be another α-cellulose containing pulp, such as viscose grade pulp, rayon grade pulp, semi-bleached pulp, unbleached pulp, bleach pulp, kraft pulp, absorbent pulp, dissolving-grade pulp, or fluff. While these cellulosic materials comprise various concentrations of α-cellulose, the inventive processes may advantageously treat them, based on an optimized process design, to produce higher purity α-cellulose products.

Cellulose is a straight chain polymer and is derived from D-glucose units, which condense through β-1,4-glycosidic bonds. This linkage motif contrasts with that for α-1,4-glycosidic bonds present in starch, glycogen, and other carbohydrates. Unlike starch, there is no coiling or branching in cellulose and cellulose adopts an extended and rather stiff rod-like conformation, which is aided by the equatorial conformation of the glucose residues. The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen atoms on the same or on a neighboring chain, holding the chains firmly together side-by-side and forming microfibrils with high tensile strength, which then overlay to form the macrostructure of a cellulose fiber. In preferred embodiments of the invention, the finished cellulosic product retains its fiber structure throughout and after the extraction step.

As used herein, the term “hemicellulose” refers to any of several heteropolymers, e.g., polysaccharides, present in plant cell walls. Hemicellulose can include any one of xylan, glucuronoxylan, arabinoxylan, glucomannan, galactomannan, and xyloglucan. These polysaccharides contain many different sugar monomers and can be hydrolyzed to monosaccharides, such as xylose, mannose, galactose, rhamnose and arabinose. Xylose is typically the primary sugar present in hardwoods and either mannose or xylose is the primary sugar present in softwoods.

The processes of the present invention are particularly beneficial in that they are effective for use with paper grade wood pulp that is derived from softwoods and hardwoods. The processes of the present invention provide a technique for recovering dissolving-grade pulp compositions and also for recovering a hemicellulose composition produced from hardwood and softwood species.

Softwood species are generally more abundant and faster growing than most hardwood species. Softwood is a generic term typically used in reference to wood from conifers (i.e., needle-bearing trees from the order Pinales). Softwood-producing trees include pine, spruce, cedar, fir, larch, douglas-fir, hemlock, cypress, redwood and yew. Conversely, the term hardwood is typically used in reference to wood from broad-leaved or angiosperm trees. The terms “softwood” and “hardwood” do not necessarily describe the actual hardness of the wood. While, on average, hardwood is of higher density and hardness than softwood, there is considerable variation in actual wood hardness in both groups, and some softwood trees can actually produce wood that is harder than wood from hardwood trees. One feature separating hardwoods from softwoods is the presence of pores, or vessels, in hardwood trees, which are absent in softwood trees. On a microscopic level, softwood contains two types of cells, longitudinal wood fibers (or tracheids) and transverse ray cells. In softwood, water transport within the tree is via the tracheids rather than the pores of hardwoods.

IV. Extractant

As described above, hemicellulose, and optionally degraded cellulose, is extracted from the cellulosic material using an extractant. The extractant comprises a cellulose solvent and a co-solvent. The cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and mixtures thereof, examples of which are described below. The cellulose solvent may or (more preferably) may not fully dissolve α-cellulose, but preferably dissolves at least hemicellulose and degraded cellulose. α-cellulose preferably is less soluble in the co-solvent than in the cellulose solvent.

a. Ionic Liquid

Ionic liquids are organic salts with low melting points, preferably less than 200° C., less than 150° C., or less than 100° C., many of which are consequently liquid at room temperature. Specific features that make ionic liquids suitable for use in the present invention are their general lack of vapor pressure, their ability to dissolve a wide range of organic compounds and the versatility of their chemical and physical properties. In addition, ionic liquids are non-flammable making them particularly suitable for use in industrial applications. In some embodiments, the cellulose solvent comprises one or more ionic liquids.

It has been found that, in addition to these beneficial properties, when contacted with cellulosic materials, including plant matter and plant matter derivatives, the ionic liquids are capable of acting as a cellulose solvent, dissolving the hemicellulose and cellulose contained therein. In addition, with the appropriate choice of treatment conditions (for example, duration of contact, temperature, and co-solvent composition), ionic liquids penetrate the structure of the cellulose-containing material to break down the material and extract organic species therein. In particular when used in combination with one or more co-solvents, α-cellulosic components remaining in the cellulosic material are preserved and the fiber morphology is advantageously retained.

Ionic liquids, in pure form, generally are comprised of ions and do not necessitate a separate solvent for ion formation. Ionic liquids existing in a liquid phase at room temperature are called room temperature ionic liquids. Generally, ionic liquids are formed of large-sized cations and a smaller-sized anion. Cations of ionic liquids may comprise nitrogen, phosphorous, sulfur, or carbon. Because of the disparity in size between the cation and anion, the lattice energy of the compound is decreased resulting in a less crystalline structure with a low melting point.

Exemplary ionic liquids include the compounds expressed by the following Formula (1):

[A]⁺[B]⁻  (1)

In one embodiment, the ionic liquid is selected from the group consisting of substituted or unsubstituted imidazolium salts, pyridinium salts, ammonium salts, triazolium salts, pyrazolium salt, pyrrolidinium salt, piperidium salt, and phosphonium salts. In preferred embodiments, [A]⁺ is selected from the group consisting of:

wherein R₁, R₂, R₃, R₄, R₅, R₆ and R₇ are each independently selected from the group consisting of hydrogen, C₁-C₁₅ alkyls, C₂-C₁₅ aryls, and C₂-C₂₀ alkenes, and the alkyl, aryl or alkene may be substituted by a substituent selected from the group consisting of sulfone, sulfoxide, thioester, ether, amide, hydroxyl and amine. [B]⁻ is preferably selected from the group consisting of Cl⁻, Br⁻, I⁻, OH⁻, NO₃ ⁻, SO₄ ²⁻, CF₃CO₂ ⁻, CF₃SO₃ ⁻, BF₄ ⁻, PF₆ ⁻, CH₃COO⁻, (CF₄SO₂)₂N⁻, AlCl₄ ⁻, HCOO⁻, CH₃SO₄ ⁻, (CH₃)₂PO₄ ⁻, (C₂H₅)₂PO₄ ⁻ and CH₃HPO₄ ⁻.

Examples of ionic liquids include tetrabutylammonium hydroxide 30 hydrate (TBAOH.30H₂O), benzyltriethylammonium acetate (BnTEAAc), tetraethylammonium acetate tetrahydrate (TEAAc.4H₂O), benzyltrimethylammonium hydroxide (BnTMAOH), tetramethylammonium hydroxide (TMAOH), ammonium acetate, hydroxyethylammonium acetate, hydroxyethylammonium formate, tetramethylammonium acetate, tetraethylammonium acetate, tetrabutylammonium acetate, tetrabutylammonium hydroxide, 1-butyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1,3-diethylimidazolium acetate (EEIMAc), 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, and mixtures or complexes thereof, but the disclosed concept of utilizing ionic liquids is not limited to the disclosed species.

In some embodiments, the ionic liquid is selected from the group consisting of ammonium-based ionic substances, imidazolium-based ionic substances, phosphonium-based ionic substances, and mixtures thereof. The ammonium-based ionic liquid may be selected from the group consisting of ammonium acetate, hydroxyethylammonium acetate, hydroxyethylammonium formate, tetramethylammonium acetate, tetrabutylammonium acetate, tetraethylammonium acetate, benzyltriethylammonium acetate, benzyltributyl ammonium acetate and combinations thereof. The imidazolium-based ionic liquid may be selected from the group consisting of 1-butyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1,3-diethylimidazolium acetate (EEIMAc), 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate (EMIMDEP), 1,3-dimethylimidazolium dimethyl phosphate (DMIMDMP) and mixtures or complexes thereof. The ionic liquid may also be selected from the group consisting of N,N-dimethylpyrrolidinium acetate, N,N-dimethylpiperidinium acetate, N,N-dimethylpyrrolidinium dimethyl phosphate, N,N-dimethylpiperidinium dimethyl phosphate, N,N-dimethylpyrrolidinium chloride, N,N-dimethylpiperidinium chloride, and combinations thereof.

In still other embodiments, the ionic liquid may be selected from the group consisting of 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate, 1,3-dimethylimidazolium dimethyl phosphate and combinations and complexes thereof.

In further embodiments, the ionic liquid may be selected from the group consisting of ethyltributylphosphonium diethylphosphate, methyltributylphosphonium dimethylphosphate, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tributylmethylphosphonium methylsulfate, trihexyltetradecylphosphonium decanoate, trihexyltetradecylphosphonium dicyanamide, ethyltriphenylphosphonium acetate, ethyltributylphosphonium acetate, benzyltriethylphosphonium acetate, benzyltributylphosphonium acetate, tetrabutylphosphonium acetate, tetraethylphosphonium acetate, tetramethylphosphonium acetate, and combinations thereof.

The ionic liquid may be commercially available, and may include Basionic™ AC 01, Basionic™ AC 09, Basionic™ AC 25, Basionic™ AC 28, Basionic™ AC 75, Basionic™ BC 01, Basionic™ BC 02, Basionic™ FS 01, Basionic™ LQ 01, Basionic™ ST 35, Basionic™ ST 62, Basionic™ ST 70, Basionic™ ST 80, Basionic™ VS 01, and Basionic™ VS 02, but the invention is not limited to use of these species.

In preferred embodiments, the ionic liquid compound, as shown below, may be 1-ethyl-3-methyl imidazolium acetate (EMIMAc) of the structural formula (2), 1-butyl-3-methyl imidazolium acetate (BMIMAc) of the structural formula (3), 1-ethyl-3-methyl imidazolium dimethylphosphate of structural formula (4), 1-ethyl-3-methyl imidazolium formate of the structural formula (5), tetrabutylammonium acetate (TBAAc) of the structural formula (6), 1-allyl-3-methyl imidazolium chloride of the structural formula (7), or 1-n-butyl-3-methyl imidazolium chloride of the structural formula (8):

b. Amine Oxide

Amine oxides are chemical compounds that contain the functional group R₃N⁺—O⁻, which represents an N—O bond with three additional hydrogen and/or hydrocarbon side chains. Amine oxides are also known as tertiary amines, N-oxides, amine-N-oxide and tertiary amine N-oxides. In one embodiment, amine oxides that are stable in water may be used.

In some embodiments, the amine oxide may be selected from the group consisting of compounds with chemical structure of acyclic R₃N⁺—O⁻, compounds with chemical structure of N-heterocyclic compound N-oxide, and combinations thereof. In further embodiments, the amine oxide may be an acyclic amine oxide compound with structure of R₁R₂R₃N⁺—O⁻, wherein R₁, R₂ and R₃ are alkyl or aryl chains, the same or different, with chain length from 1 to 18, e.g. trimethylamine N-oxide, triethylamine N-oxide, tripropylamine, N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, monomethyldiethylamine, dimethylmonoethylamine, monomethyldipropylamine, N-dimethyl-, N-diethyl- or N-dipropylcyclohexylamine, N-dimethylmethylcyclohexylamine, pyridine, and pyridine N-oxide.

In some embodiments, the amine oxide may be a cyclic amine oxide compound including the structures such as pyridine, pyrrole, piperidine, pyrrolidine and other N-heterocyclic compounds, e.g. N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide. In some embodiments, the amine oxide may be the combination of the above mentioned acyclic and/or cyclic amine oxides.

In specific embodiments, the amine oxide may be selected from the group consisting of trimethylamine N-oxide, triethylamine N-oxide, tripropylamine N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide, and combinations thereof.

Cellulose is insoluble in most solvents because of its strong and highly structured intermolecular hydrogen bonding network. Without being bound by theory, NMMO is able to break the hydrogen bonding network that keeps cellulose insoluble in most solvents. Therefore, the use of NMMO alone would destroy the fiber morphology of cellulose. It has now been discovered that by using the proper ratio of an amine oxide, such as NMMO, with a co-solvent, α-cellulosic components in the cellulosic material may be beneficially preserved and the fiber morphology retained. NMMO is typically stored in 50 to 70 vol. %, e.g., 60 vol. %, aqueous solution as pure NMMO tends toward oxygen separation. See, e.g., U.S. Pat. No. 4,748,241, the entirety of which is incorporated herein by reference. Further contaminants in commercial NMMO product, e.g., N-methylmorpholine, peroxides, and acid components, tend to degrade the storage stability. In other words, further application of NMMO needs to address all stability concerns. For example, developed stabilizers like propyl gallate may be added.

c. Co-Solvent

As stated above, the extractant also comprises a co-solvent. Co-solvents in the context of this invention include solvents that do not have the ability to readily dissolve α-cellulose. In exemplary embodiments, the co-solvent is selected, with various concentrations, from the group consisting of water, acetic acid, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, diols and polyols such as ethanediol and propanediol, amino alcohols such as ethanolamine, diethanolamine and triethanolamine, aromatic solvents, e.g., benzene, toluene, ethylbenzene or xylenes, halogenated solvents, e.g. dichloromethane, chloroform, carbon tetrachloride, dichloroethane or chlorobenzene, aliphatic solvents, e.g. pentane, hexane, heptane, octane, ligroin, petroleum ether, cyclohexane and decalin, ethers, e.g. tetrahydrofuran, diethyl ether, methyl tert-butyl ether and diethylene glycol monomethyl ether, ketones such as acetone and methyl ethyl ketone, esters, e.g. ethyl acetate, dimethyl carbonate, dipropyl carbonate, propylene carbonate, amides, e.g., formamide, dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), DMSO, acetonitrile and mixtures thereof. Since the boiling points of co-solvents vary significantly, the efficient purification processes associated with each co-solvent may not be exactly the same.

In one embodiment, a second co-solvent may be used in conjunction with the first co-solvent and the cellulose solvent, e.g., amine oxide or ionic liquid, as described above. In one embodiment, the second co-solvent decreases the viscosity of the extractant. The second co-solvent may have a viscosity, for example, of less than 2.0 mPa·s, e.g., less than 1.8 mPa·s or less than 1.5 mPa·s at 25° C. In some embodiments, the second co-solvent is selected from the group consisting of formamide, DMF, dimethylacetamide, DMSO, N-methylpyrrolidone, propylene carbonate, acetonitrile and mixtures thereof. It is postulated that using a low viscosity second co-solvent in the extractant, the extraction rate is enhanced and a smaller amount of ionic liquid is needed to extract the hemicellulose in the cellulosic material.

Without being bound by theory, the insolubility of the α-cellulose in the co-solvent and the resulting extractant maintains the cellulose fiber morphology, e.g., leaving the fiber morphology unchanged, while the extractant penetrates the cellulosic material, dissolves and extracts the hemicellulose and preferably degraded cellulose from the cellulosic material. Depending on the specific co-solvent used in the extractant, the weight percentage of the cellulose solvent and the co-solvent in the extractant may vary widely.

d. Extractant Compositions

The specific formulation of the extractant employed may vary widely, depending, for example, on the hemicellulose and degraded cellulose content of the starting cellulosic material, and the processing scheme employed. In one embodiment, the extractant optionally comprises at least 0.1 wt. % amine oxide, e.g., at least 2 wt. % or at least 4 wt. %. In terms of upper limits, the extractant optionally comprises at most 85 wt. % amine oxide, e.g., at most 75 wt. %, or at most 70 wt. % amine oxide. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 85 wt. % amine oxide, e.g., from 2 wt. % to 75 wt. %, or from 4 wt. % to 70 wt. %. The extractant optionally comprises at least 0.1 wt. % co-solvent, e.g., at least 1 wt. %, or at least 3 wt. % co-solvent. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. %, at most 98 wt. %, or at most 97 wt. % co-solvent. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 99.9 wt. % co-solvent, e.g., from 1 wt. % to 98 wt. %, or from 3 wt. % to 97 wt. % co-solvent.

In one embodiment, the extractant comprises an aqueous co-solvent, e.g., water, and an amine oxide. For example, the extractant optionally comprises at least 40 wt. % amine oxide, e.g., at least 50 wt. % or at least 60 wt. %. In terms of upper limits, the extractant optionally comprises at most 90 wt. % amine oxide, e.g., at most 85 wt. %, or at most 80 wt. % amine oxide. In terms of ranges, the extractant optionally comprises from 40 wt. % to 90 wt. % amine oxide, e.g., from 50 wt. % to 85 wt. %, or from 60 wt. % to 80 wt. % amine oxide. The extractant optionally comprises at least 1 wt. % aqueous co-solvent, e.g., at least 5 wt. %, or at least 10 wt. % aqueous co-solvent. In terms of upper limits, the extractant optionally comprises at most 50 wt. % aqueous co-solvent, at most 40 wt. %, or at most 30 wt. %. In terms of ranges, the extractant optionally comprises from 1 wt. % to 50 wt. % aqueous co-solvent, e.g., from 5 wt. % to 40 wt. %, or from 10 wt. % to 30 wt. %.

In one embodiment, the extractant comprises an organic co-solvent and an amine oxide. In this aspect, the extractant optionally comprises at least 0.1 wt. % amine oxide, e.g., at least 1 wt. % or at least 2 wt. % amine oxide. In terms of upper limits, the extractant optionally comprises at most 85 wt. % amine oxide, e.g., at most 80 wt. %, or at most 70 wt. %. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 85 wt. % amine oxide, e.g., from 1 wt. % to 80 wt. %, or from 2 wt. % to 70 wt. %. In this aspect, the extractant optionally comprises at least 15 wt. % organic co-solvent, e.g., at least 20 wt. %, or at least 30 wt. %. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. % organic co-solvent, at most 98 wt. %, or at most 97 wt. %. In terms of ranges, the extractant optionally comprises from 15 wt. % to 99.9 wt. % organic co-solvent, e.g., from 20 wt. % to 98 wt. %, or from 30 wt. % to 97 wt. %. In one embodiment, the organic co-solvent is DMSO.

In one embodiment, the extractant includes an amine oxide, a first co-solvent and a second co-solvent. In one embodiment, the extractant includes an amine oxide, an aqueous co-solvent, e.g., water, and an organic co-solvent, e.g., DMSO. In this aspect, the amine oxide concentration may range, for example, from 1 wt. % to 85 wt. %, the water concentration may range from 1 wt. % to 35 wt. %, and the organic co-solvent, e.g., DMSO, concentration may range from 1 wt. % to 98 wt. %.

In other embodiments, the cellulose solvent used in the extractant comprises one or more ionic liquids. For example, the extractant optionally comprises at least 0.1 wt. % ionic liquid, e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper limits, the extractant optionally comprises at most 95 wt. % ionic liquid, e.g., at most 90 wt. %, or at most 85 wt. %. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 95 wt. % ionic liquid, e.g., from 1 wt. % to 90 wt. %, or from 2 wt. % to 85 wt. %. The extractant optionally comprises at least 5 wt. % co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, or at least 20 wt. %. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. % co-solvent, at most 99 wt. %, or at most 98 wt. %. In terms of ranges, the extractant optionally comprises from 5 wt. % to 99.9 wt. % co-solvent, e.g., from 10 wt. % to 99 wt. %, or from 20 wt. % to 98 wt. %.

In one embodiment, the cellulose solvent comprises one or more ionic liquids and the co-solvent comprises an aqueous co-solvent, e.g., water. In this aspect, the extractant preferably comprises at least 50 wt. % ionic liquid, e.g., at least 65 wt. % or at least 80 wt. %. In terms of upper limits, the extractant optionally comprises at most 95 wt. % ionic liquid, e.g., at most 90 wt. %, or at most 85 wt. %. In terms of ranges, the extractant optionally comprises from 50 wt. % to 95 wt. % ionic liquid, e.g., from 65 wt. % to 90 wt. %, or from 70 wt. % to 85 wt. %. The extractant optionally comprises at least 5 wt. % aqueous co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, or at least 20 wt. %. In terms of upper limits, the extractant optionally comprises at most 50 wt. % aqueous co-solvent, e.g., at most 35 wt. %, or at most 20 wt. % aqueous co-solvent. In terms of ranges, the extractant may comprise from 5 wt. % to 50 wt. % aqueous co-solvent, e.g., from 10 wt. % to 35 wt. %, or from 15 wt. % to 20 wt. %.

In one embodiment, when the extractant comprises one or more ionic liquids as cellulose solvent and an organic co-solvent, the extractant preferably comprises at least 0.1 wt. % ionic liquid, e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper limits, the extractant optionally comprises at most 20 wt. % ionic liquid, e.g., at most 15 wt. %, or at most 10 wt. %. In terms of ranges, the extractant may comprise from 0.1 wt. % to 20 wt. % ionic liquid, e.g., from 1 wt. % to 15 wt. %, or from 2 wt. % to 10 wt. %. The extractant optionally comprises at least 80 wt. % organic co-solvent, e.g., at least 85 wt. %, or at least 90 wt. %. In terms of upper limits, the extractant may comprise at most 99.9 wt. % organic co-solvent, e.g., at most 98 wt. %, or at most 97 wt. %. In terms of ranges, the extractant optionally comprises from 80 wt. % to 99.9 wt. % organic co-solvent, e.g., from 85 wt. % to 98 wt. %, or from 90 wt. % to 97 wt. %. In one embodiment, the organic co-solvent is DMSO.

In one embodiment, the extractant includes a cellulose solvent, e.g., amine oxide or ionic liquid, a first co-solvent and a second co-solvent. In this aspect, the weight ratio of first co-solvent to second co-solvent is preferably from 20:1 to 1:20, e.g. from 15:1 to 1:15 or from 10:1 to 1:10. Since the production costs of ionic liquids are generally higher than those of co-solvents, the use of a large amount of the second co-solvent beneficially reduces the cost of purifying the cellulosic material.

In one embodiment, the extractant includes an ionic liquid, a first co-solvent and a second co-solvent. In one embodiment, the extractant includes an ionic liquid, an aqueous co-solvent, e.g., water, and an organic co-solvent, e.g., DMSO. In the tertiary extractant system, the extractant may include at most 50 wt. % ionic liquid, e.g., at most 40 wt. %, or at most 30 wt. %. In terms of lower limit, the extractant may include at least 0.1 wt. % ionic liquid, e.g., at least 5 wt. % or at least 10 wt. %. In terms of ranges, the extractant may include from 0.1 wt. % to 50 wt. % ionic liquid, e.g., from 5 wt. % to 40 wt. %, or from 10 wt. % to 30 wt. %. In some embodiments, the extractant may include at most 20 wt. % the first co-solvent, i.e., at most 16 wt. %, or 10 wt. %. In terms of ranges the extractant may include from 0.5 wt. % to 20 wt. % the first co-solvent, e.g., from 3 wt. % to 16 wt. % or from 5 wt. % to 10 wt. %. In one embodiment, water is the first co-solvent. In one embodiment, DMSO is the second co-solvent. Without being bound by theory, it is postulated that the decrease in viscosity in the extractant by using the second co-solvent beneficially enhances the extraction rate and increases the amount of hemicellulose extracted from the cellulosic material.

In one embodiment, the extractant comprises an aqueous co-solvent, an ionic liquid and an amine oxide. In this aspect, the co-solvent concentration may range, for example, from 5 wt. % to 50 wt. %, the ionic liquid concentration may range from 0.1 wt. % to 50 wt. %, and the amine oxide concentration may range from 0.1 wt. % to 85 wt. %.

In one embodiment, the extractant comprises an organic co-solvent, an ionic liquid and an amine oxide. In this aspect, the co-solvent concentration may, for example, range from 5 wt. % to 99 wt. %, the ionic liquid concentration may range from 0.1 wt. % to 50 wt. %, and the amine oxide concentration may range from 0.1 wt. % to 50 wt. %.

V. Process for Forming a Dissolving-Grade Pulp Composition

As described herein, cellulosic material may be purified through an inventive extraction process to produce a dissolving-grade pulp composition and also to recover hemicellulose from a cellulosic material. FIG. 1 illustrates one non-limiting exemplary system for purifying a cellulosic material, and recovering a hemicellulose composition. As shown in FIG. 1, the cellulosic material may be purified in purification process 100. As shown, the cellulosic material is fed via line 103 to extractor 105. Line 103 may represent, for example, a pneumatic lock hopper, a screw feeder, a belt feeder, a rotary valve feeder, or another type of solid transport equipment. Extractant, comprising a cellulose solvent and co-solvent, as described above, is fed to extractor 105 via line 104. Although cellulosic material 103 and extractant 104 are shown as fed separately to extractor 105, it is contemplated that they may be completely or partially mixed prior to being fed to extractor 105. As shown in FIG. 1, cellulosic material 103 and extractant 104 may be combined in extractor 105 to form an extraction mixture. The extraction mixture within extractor 105 may comprise, for example, from 0.1 to 20 wt. % solids, e.g., from 0.5 to 15 wt. % or from 1.25 to 10 wt. % solids.

Extractant 104 for extracting cellulosic material 103 may be any extractant capable of dissolving preferably at least 50% of the hemicellulose, more preferably at least 75% or at least 90% of the hemicellulose, in cellulosic material 103, as determined by UV absorbance analysis of hemicellulose concentration for hardwood and mass measurements of the feed, cellulosic product, and hemicellulose product. Extractant 104 comprises a cellulose solvent and co-solvent in relative amounts that do not overly degrade or dissolve the cellulose. For example, in one embodiment, the extractant dissolves less than 15% of the α-cellulose in cellulosic material 103, e.g., less than 10%, or less than 5%, as determined similarly by UV absorbance analysis and mass measurements.

As described above, amine oxides and ionic liquids may tend to dissolve α-cellulose. The extractant preferably comprises sufficient co-solvent to reduce α-cellulose solubility in the overall extractant to a point that the α-cellulose does not readily dissolve therein. Preferably, the α-cellulose is substantially insoluble in the co-solvent. Extractant 104 in accordance with the present invention, therefore, has the property of selectively dissolving the hemicellulose and preferably degraded cellulose that is in cellulosic material 103.

Exemplary compositions for the cellulosic material and extractant fed to the extractor, and for the resulting extraction mixture are provided in Table 1.

TABLE 1 EXTRACTOR 105 Conc. Conc. Conc. (wt. %) (wt. %) (wt. %) Cellulosic Material 103 “Cellulose”* 50 to 90  55 to 85 60 to 80 “Hemicellulose”**  1 to 40  5 to 30 10 to 25 Water 0.1 to 49   1 to 40  1 to 29 Extractant 104 Solvent  0.1 to 99.9  2 to 90  3 to 80 Co-solvent  0.1 to 99.9  10 to 98 20 to 97 Extraction Mixture in Extractor 105 Cellulose 0.3 to 14  0.3 to 13 0.3 to 12  Hemicellulose*** 0.005 to 6    0.03 to 5  0.05 to 4   Water 0.001 to 3    0.005 to 3   0.005 to 2    Solvent 0.09 to 99.4 1.7 to 90 2.6 to 80  Co-solvent 0.09 to 99.4 8.5 to 98 17 to 97 *“Cellulose” refers to cellulose of all forms including degraded cellulose **“Hemicellulose” in cellulosic material 103 refers to hemicellulose alone excluding non-hemicellulose impurities ***“Hemicellulose” after being dissolved in extractant 104 refers to hemicellulose, degraded cellulose, and other impurities

The treatment of cellulosic material 103 with extractant 104 may be conducted at an elevated temperature, and preferably occurs at atmospheric pressure or slightly above atmospheric pressure. Preferably, the contacting is conducted at a temperature from 30° C. to 300° C., e.g., from 40° C. to 200° C., or from 50° C. to 150° C. In terms of upper limits, the treatment of cellulosic material 103 may be conducted at a temperature of less than 300° C., e.g., less than 200° C., or less than 150° C. In terms of lower limit, the treatment of cellulosic material 103 may be conducted at a temperature of greater than 30° C., e.g., greater than 40° C., or greater than 50° C. The pressure (absolute, unless otherwise indicated) is in the range from 100 kPa to 10 MPa, preferably from 100 kPa to 5000 kPa, more preferably from 100 kPa to 1100 kPa. In some embodiments, the pressure may be reduced below 100 kPa, e.g., from 1 to 99 kPa.

Cellulosic material 103 may contact extractant 104 (or have a residence time in extractor 105 for continuous processes) between 5 minutes to 1000 minutes, e.g., between 20 minutes to 500 minutes, or from 40 minutes to 200 minutes. In terms of lower limits, the treatment of cellulosic material 103 may be for at least 5 minutes, e.g., at least 20 minutes or at least 40 minutes. In terms of upper limits, the treatment of cellulosic material 103 may be for at most 1000 minutes, e.g., at most 500 minutes, or at most 200 minutes.

The extraction process may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In a continuous process, cellulosic material 103 contacts extractant 104 in one or more extraction vessels. In one embodiment, extractant 104 may be heated to the desired temperature before contacting cellulosic material 103. In one embodiment, the extraction vessel(s) may be heated by any suitable means to the desired temperature. Additionally, an inert gas (not shown), e.g., nitrogen or CO₂, may be supplied to the extractor to improve turbulence in the extractor and thus improving heat and mass transfers. The flow rate of inert gas will be controlled not to cause hydrodynamic problem, e.g. flooding. When the size and concentration of solid materials along with the flow rate of inert gas are well controlled, the addition of an inert gas may cause the solids in extractor 105 to float on the surface of the extraction mixture allowing for the solids to be skimmed off the surface of the liquid phase contained in extractor 105.

In the extraction step, the mass ratio of extractant to cellulosic material may range from 5:1 to 500:1, e.g., from 7:1 to 300:1, or from 10:1 to 100:1. The solid:liquid volume ratio may range from 0.005:1 to 0.17:1, e.g., from 0.01:1 to 0.15:1 or from 0.02:1 to 0.1:1, depending on the extraction apparatus and set-up. In one embodiment, a solid:liquid ratio of from 0.01:1 to 0.02:1 or about 0.0125:1 may be used to facilitate the filtration operation in a batch process. In another embodiment, a solid:liquid ratio of 0.1:1 to 0.17:1 can be used, in particular for extractors employing countercurrent extraction. The amount of extractant employed has a significant impact on process economics. Counter-current extraction may achieve greater extraction efficiency while maintaining reasonable extractant usage. Counter-current extraction of solubles from pulp can be accomplished in a variety of commercial equipment such as, but not limited to, a series of agitated tanks, hydrapulpers, continuous belt extractors, and screw extractors. Twin-screw extractors are generally more efficient than single-screw extractors. After extraction, the separation of solid and liquid phases can be completed in suitable commercial equipment, which includes filters, centrifuges, and the like.

In one embodiment, the cellulosic material is subjected to repeated extraction steps. For example, the cellulosic material may be treated with the extractant in an initial extraction step followed by one or more additional extraction steps, in the same or multiple extractors, to further extract residual hemicellulose and/or degraded cellulose. In one embodiment, the cellulosic product may be subjected to an initial extraction step, followed by an extractant wash step, followed by a second extraction step. In some embodiments, the cellulosic product may be subjected to a third or fourth extraction step. When multiple extraction steps are employed, the extractant in each extraction step may be the same or varied to account for the different concentrations of hemicellulose and degraded cellulose in intermediate cellulosic materials between extraction steps. For example, a first extraction may use an extractant comprising an ionic liquid and a co-solvent and a second extraction may use an extractant comprising an amine oxide and a co-solvent, or vice versa, optionally with one or more extractant wash steps between and/or after the second extraction step. Similar configurations can be designed and optimized based upon the general chemical engineering principles and process design theory.

In another embodiment (not shown), the process may further include enzymatic digestion of hemicellulose, extraction and/or isolation of digested hemicellulose and recovery of a cellulosic product with reduced hemicellulose content. Without being bound by theory, by treating the cellulosic material first with the extractant, enzymes may be better able to penetrate the cellulosic material to hydrolyze residual hemicellulose and/or degraded cellulose contained therein. On the contrary, experimental data has shown that less hemicellulose may be removed from the cellulosic material if it is first treated with an enzyme cocktail under optimum enzyme hydrolysis conditions, followed by an extraction step. For enzymes to be effective in hydrolyzing hemicellulose, a pretreatment step (e.g., prehydrolysis) is preferred in order to make the cellulosic materials amenable to enzymatic hydrolysis. The pretreatment step preferably comprises treating the cellulosic material with high pressure steam, optionally at low or high acid concentrations, or ammonia treatment. Some modification to the process flow scheme may be desired since the enzyme treatment would likely necessitate increased residence time to complete enzymatic hydrolysis. In addition, acidity (pH), temperature and ionic strength would likely need to be adjusted for effective enzymatic treatment.

In this embodiment, after the extraction step, the cellulosic material may be treated with an enzyme, preferably a hemicellulase, to break down residual hemicellulose contained in the cellulosic material. The hemicellulase includes one or more enzymes that hydrolyze hemicellulose to form simpler sugars, ultimately yielding monosaccharides, such as glucose, hexoses and pentoses. Suitable hemicellulase include one or more of xyloglucanase, β-xylosidase, endoxylanase, α-L-arabinofuranosidase, α-glucuronidase, mannanase, and acetyl xylan esterase. Preferably, the enzymes include a combination of both endo-enzymes (i.e., enzymes hydrolyzing internal polysaccharide bonds to form smaller poly- and oligosaccharides) and exo-enzymes (i.e., enzymes hydrolyzing terminal and/or near-terminal polysaccharide bonds) to facilitate the rapid hydrolysis of large polysaccharide molecules. Suitable commercial hemicellulase include SHEARZYME (available from Novozymes A/S, Bagsvaerd, Denmark), PULPZYME (available from Novozymes A/S, Bagsvaerd, Denmark), FRIMASE B210 (available from Puratos, Groot-Bijgaarden, Belgium), FRIMASE B218 (available from Puratos, Groot-Bijgaarden, Belgium), GRINDAMYL (available from Danisco, Copenhagen, Denmark), ECOPULP TX200A (available from AB Enzymes, Darmstadt, Germany), MULTIFECT Xylanase (available from Genencor/Danisco, Palo Alto, USA), PENTOPAN Mono BG (available from Novozymes, Bagsvaerd, Denmark), and PENTOPAN 500 BG (available from Novozymes, Bagsvaerd, Denmark).

The enzymes generally can be used in amounts that are not particularly limited. For example, hemicellulase can be used in amounts ranging from about 0.001 mg/g to about 500 mg/g (e.g., about 0.05 mg/g to about 200 mg/g, about 0.1 mg/g to about 100 mg/g, about 0.2 mg/g to about 50 mg/g, or about 0.3 mg/g to about 40 mg/g). The concentration units are milligrams of enzyme per gram of cellulosic material to be treated.

After the desired contacting time, an extraction mixture is removed from extractor 105 via line 106. The extraction mixture 106 comprises extractant, dissolved hemicellulose, dissolved degraded cellulose, side products, e.g., mono-, di-, and oligo-saccharide, and an intermediate cellulosic material having reduced hemicellulose content and preferably reduced degraded cellulose content. As shown in FIG. 1, extraction mixture 106 may be fed to filter/washer 108 to remove extractant, dissolved hemicellulose, and dissolved degraded cellulose. Removal of the extractant in the filtering step reduces the amount of residual hemicellulose that must be further processed with the intermediate cellulosic material. It also reduces the amount of extractant that must be separated from the intermediate cellulose in subsequent steps. Filter/washer 108 may comprise solid-liquid separation equipment, including but not limited to, for example, rotary vacuum drums, belt filters and screw presses. Filter/washer 108 forms a washed intermediate cellulosic material 114 and an extraction filtrate 109.

Prior to exiting filter/washer 108, optionally while on a vacuum belt filter, the intermediate cellulosic material may be washed with extractant wash 107 to further reduce the amount of extractant remaining in the filtered extraction mixture. The washing may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In some embodiments, the intermediate cellulosic material may be washed more than once in separate washing units from filter/washer 108. When more than one washing step is used, the composition of the extractant wash may vary in the different washing steps. For example, a first washing step may use DMSO as an extractant wash to remove residual hemicellulose and ionic liquid and a second washing step may use water as an extractant wash to remove residual DMSO. A similar configuration can be designed and optimized based upon the general chemical engineering principles and process design theory.

Extractant wash 107 preferably comprises a co-solvent, which dissolves residual hemicellulose and/or degraded cellulose from the cellulosic material, but may also include some low level of extractant resulting from the sequence of washing steps. In one embodiment, the extractant wash is selected from the group consisting of water, acetonitrile, DMF, DMAC, ketones (e.g. acetone), aldehydes, esters (e.g. methyl acetate, ethyl acetate), ethers (e.g., MTBE), lactones, carboxylic acids (e.g., acetic acid), alcohols, polyols, amino alcohols, DMSO, formamide, propylene carbonate, aromatic solvents, halogenated solvents, aliphatic solvents, vinyl acetate, nitriles (propionitrile, chloroacetonitrile, butyonitrile), chloroform, dichloromethane, and mixtures thereof. In another embodiment, extractant wash 107 is selected from the group consisting of DMSO, DMF, N-methyl pyrrolidone, methanol, ethanol, isopropanol, dimethyl carbonate, propylene carbonate, acetone, water, and mixtures thereof. In some embodiments, at least two extractant washes are used in series, such as DMSO and water. It should be understood that, depending on the amount of residual hemicellulose contained in the cellulosic material, the amount of extractant wash may be minimized to reduce capital cost and energy requirements for subsequent separation and recycle, described below. Additionally, it should be understood that the one or more extractant washes may also be used to remove side products, e.g., mono-, di-, and oligo-saccharides from the extraction mixture.

The extractant wash may further comprise one or more washing aids that improve the removal of extractant from the cellulosic material, improve operability, or otherwise improve the physical properties of the intermediate cellulose material. The washing aids may include, for example, defoamers, surfactants, and mixtures therefore. The amount of washing agent can vary widely based upon the amount of residual extractant, quality requirement for cellulosic product, and process operability.

The extractant wash may then be removed via line 113, e.g., as used extractant wash filtrate. The washed intermediate cellulosic material exits filter/washer 108 as an intermediate cellulosic material 114 having reduced hemicellulose content and preferably reduced degraded cellulose content. Intermediate cellulosic material 114 may comprise less than 6 wt. % extractant, e.g., less than 5 wt. % or less than 4 wt. % extractant. In some embodiments, the intermediate cellulosic material 112 may comprise less than 0.5 wt. % cellulose solvent (ionic liquid and/or amine oxide), e.g., less than 0.05 wt. %, less than 0.005 wt. %, or less than 0.001 wt. %. Intermediate cellulosic material 112 may comprise from 9.9 to 99% solids, e.g., from 19 to 90% or from 28 to 85%.

Exemplary compositions using DMSO as the co-solvent and water as the extractant wash for the intermediate cellulosic material are provided in Table 2. When DMSO is used as the co-solvent and water is used as the extractant wash, at least 90% of the cellulose in cellulosic material 103 is maintained in cellulose product 116, as described herein.

TABLE 2 FILTER/WASHER 108 Conc. Conc. Conc. (wt. %) (wt. %) (wt. %) Extraction Mixture 106 Cellulose 0.24 to 14  0.26 to 13  0.29 to 12  Hemicellulose* 0.008 to 7    0.03 to 5  0.05 to 5   Solvent (e.g., Ionic 0.09 to 99.4 1.7 to 90 2.6 to 80  Liquid) Co-solvent (e.g., 0.09 to 99.4 8.5 to 98 17 to 97 DMSO) Washed Intermediate Cellulosic Material 114 Cellulose 9.9 to 99   19 to 90 28 to 85 Hemicellulose* 0.003 to 12   0.02 to 9  0.06 to 7   Extractant wash (e.g.,  1 to 90  10 to 80 15 to 70 water) Extraction Filtrate 109 Cellulose 0.002 to 1.4  0.003 to 1.3  0.003 to 1.2  Hemicellulose* 0.008 to 6.7  0.03 to 5.2  0.05 to 4.4  Solvent (e.g., Ionic 0.09 to 99.9 1.7 to 90 2.6 to 80  Liquid) Co-solvent (e.g., 0.09 to 99.9  8.5 to 99.6 17.0 to 99.3 DMSO) Used Extractant wash (Filtrate) 113 Water  91 to 99.8  93 to 99.7  94 to 99.7 Solvent (e.g., Ionic 0.004 to 2.7  0.004 to 2.0  0.004 to 1.5  Liquid) Co-solvent (e.g., 0.01 to 2.7  0.02 to 2.2  0.03 to 1.9  DMSO) *“Hemicellulose” in these streams includes hemicellulose, degraded cellulose and other impurities

In another aspect, as shown in FIGS. 2 and 3, which depict purification processes 101 and 102, filter/washer 108 is replaced with filter 110. In this aspect, extraction mixture 106 is sent to filter 110 to form filtered intermediate cellulosic material 112 and extraction filtrate 111. Exemplary compositions using acetonitrile as the co-solvent are provided in Table 3.

TABLE 3 FILTER 110 Conc. Conc. Conc. (wt. %) (wt. %) (wt. %) Extraction Mixture 106 Cellulose 0.2 to 14  0.3 to 13 0.3 to 12 Hemicellulose*** 0.008 to 7    0.03 to 5  0.05 to 4  Water 0.001 to 10   0.01 to 8  0.1 to 5  Solvent 0.09 to 99.4 1.7 to 90 2.6 to 80 Co-solvent (e.g., 0.09 to 99.4 8.5 to 98  17 to 97 Acetonitrile) Intermediate Cellu- losic Material 112 Cellulose 25 to 80  29 to 79  33 to 78 Hemicellulose* 0.003 to 15   0.02 to 10  0.05 to 8  Solvent (e.g., Ionic 0.02 to 70  0.34 to 63  0.51 to 56  Liquid) Co-solvent (e.g., 0.02 to 70  1.7 to 68 3.4 to 68 Acetonitrile) Water 0.0003 to 7    0.002 to 6   0.02 to 4  Extraction Filtrate 111 Cellulose 0.002 to 5.2  0.003 to 3.9  0.004 to 2.9  Hemicellulose* 0.01 to 5.6  0.05 to 5.5  0.07 to 5.4  Solvent (e.g., Ionic 0.08 to 99.3 1.7 to 90  2 to 80 Liquid) Co-solvent (e.g., 0.08 to 99.3    8 to 97.4  16 to 96.4 Acetonitrile)

Intermediate cellulosic material 114 may then be further de-liquored, e.g., mechanically concentrated in a concentrator 115 to form a concentrated cellulosic material 117 having an increased solids content and a residual extractant wash 116, which may be recycled to and combined with either extractant wash 107 or stream 112. The solids content in concentrated cellulosic material 117 may range from 10 to 99 wt. %, e.g., from 20 to 90 wt. % or from 30 to 85 wt. %. The concentrator may include squeeze rolls, rotating rolls, and/or ringer rolls as well as optional heat exchangers to vaporize the liquids. Additional water removal methods may be used to concentrate the cellulosic material, depending on the desired solids content and available energy supply. The concentrated cellulosic material may comprise from 2 to 99 wt. % cellulose (e.g., from 3 to 95 wt. % cellulose), from 1 to 60 wt. % water (e.g., from 1 to 50 wt. % water), and from 0.01 to 20 wt. % hemicellulose (e.g., from 0.5 to 10 wt. % hemicellulose).

In some embodiments, when the process comprises more than one washing step, a concentrator may be utilized between washing steps or after all washing steps in order to maximize the washing separation of hemicellulose, as well as improve washing efficiency for the solvent and co-solvent thereby reducing total washing agent quantity required and associated energy and disposal costs.

Concentrated cellulosic material 117 or 114 may then be further dried in dryer 120. Hot gas may be fed to dryer 120 via line 121 and may exit dryer 120 via line 122. A finished cellulose product, e.g., dissolving-grade pulp, may then exit dryer 120 via line 123. The dryer may function to remove residual extractant wash. The finished cellulose product may comprise from 80 to 99.9 wt. % cellulose (e.g., from 90 to 95 wt. % cellulose), from 0.01 to 25 wt. % hemicellulose (e.g., from 0.1 to 15 wt. % hemicellulose) and from 0.1 to 20 wt. % water (e.g., from 3 to 15 wt. % water). Exemplary dryers include disintegrator dryers, flash dryers, apron dryers, rotary dryers, heated rolls, infrared dryers, ovens and vacuums. Without being bound by theory, the disintegrator dryer may be used to further open the cellulosic material, which may be advantageous for subsequent processing, e.g., in the formation of cellulose acetate, and derivatives thereof. In another embodiment, dryer 120 comprises heated rolls which may be used to form baled sheets or product rolls of cellulosic material. Finished cellulose product 123 may comprise less than 20 wt. % water, e.g., less than 15 wt. %, less than 10 wt. % or less than 5 wt. % water.

In another embodiment, as shown in FIG. 2, after exiting filter 110 and optional de-liquoring steps, intermediate cellulosic material 112 may be directed to washer 125 where it is washed with extractant wash 128 to further reduce the amount of extractant remaining in the intermediate cellulosic product. The washing may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In some embodiments, only one washing step is used. In other embodiments, as shown in FIG. 2, the intermediate cellulosic material may be washed more than once in separate washers 125 and 135. When more than one washing step is used, the composition of the extractant wash may vary in the different washing steps. For example, a first washing step may use co-solvent, e.g. acetonitrile as extractant wash 128 to remove residual cellulose solvent and residual hemicellulose and a second washing step may use water as extractant wash 138 to remove residual acetonitrile. A similar configuration can be designed and optimized based upon the general chemical engineering principles and process design theory and it is understood that multiple washing steps, optionally with de-liquoring and/or drying steps in between, may be used. The washing step may be conducted at a higher temperature in order to enhance mass transfer and to increase the solubility. The temperature may be from 10° C. to 100° C., e.g., from 15° C. to 90° C., or from 20° C. to 80° C.

Extractant washes 128 and 138 preferably each comprise a co-solvent, which dissolves residual cellulose solvent and residual hemicellulose and/or degraded cellulose from the cellulosic material, but may preferably be substantially free of cellulose solvent. Extractant wash 128 preferably comprises a co-solvent, which can be used to wash away the residual first co-solvent in the cellulose material. In one embodiment, the extractant wash is selected from the group consisting of acetonitrile, acetone, methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, vinyl acetate, propionitrile, dichloromethane, chloroform, butyronitrile, chloroacetonitrile, water, and combinations thereof. In other embodiments, the extract wash is selected from the group consisting of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and combinations thereof. In some embodiments, first extractant wash 128 may comprise greater than 85 wt. % acetonitrile, e.g., greater than 90 wt. % or greater than 95 wt. %; and second extractant wash 138 may comprise greater than 90 wt. % washing solvent, preferably water, e.g., greater than 95 wt. % water, greater than 99 wt. % water or greater than 99.5 wt. % water. It should be understood that, depending on the amount of residual solvent contained in the cellulosic material, the amount of extractant wash may be minimized to reduce capital cost and energy requirements for subsequent separation and recycle, described below.

The extractant wash may further comprise one or more washing aids that improve the removal of extractant from the cellulosic material, improve operability, or otherwise improve the physical properties of the intermediate cellulose material. The washing aids may include, for example, defoamers, surfactants, and mixtures thereof. The amount of washing agent can vary widely based upon the amount of residual extractant, quality requirement for cellulosic product, and process operability.

The first extractant wash may then be removed via line 127 and the second extractant wash may be removed via line 137, e.g., as used extractant wash filtrates. In some embodiments, used extractant wash filtrate 127 may be returned to extractor 105, either directly to extractor 105 or combined with solvent 104. Used extractant wash filtrate 137 may be used in hemicellulose recovery section 130. The intermediate cellulosic material exits filter 110, washer 125 and washer 135 via line 136. Washed intermediate cellulosic material 136 has reduced hemicellulose content and preferably reduced degraded cellulose content. Washed intermediate cellulosic material 136 may comprise less than 6 wt. % extractant, e.g., less than 5 wt. % or less than 4 wt. % extractant. In some embodiments, washed intermediate cellulosic material 136 may comprise less than 0.5 wt. % cellulose solvent (ionic liquid and/or amine oxide), e.g., less than 0.05 wt. %, less than 0.005 wt. %, or less than 0.001 wt. %. Washed intermediate cellulosic material 136 may comprise from 9.9 to 99% solids, e.g., from 19 to 90% or from 28 to 85%.

As shown in FIG. 3, instead of directing used extractant wash filtrate 127 directly to extractor 105 or to extractant 104, used extractant wash filtrate 127 may be separated in vaporizer 140 to form a recycled co-solvent stream 142 comprising, for example, from 60 to 95 wt. % co-solvent, e.g., from 70 to 95 wt. % or from 80 to 90 wt. % co-solvent and from 5 to 40 wt. % ionic liquid, e.g., from 7 to 30 wt. % or from 10 to 20 wt. % ionic liquid, and a second recycled co-solvent stream 141 comprising, for example, at least 90 wt. % co-solvent, e.g., at least 95 wt. %, at least 99 wt. % or at least 99.5 wt. % co-solvent. Recycled co-solvent stream 142 may be directed to extractor 105 or combined with extractant 104. Second recycled co-solvent stream 141 may be used within the process, optionally after further separation.

Exemplary compositions using acetonitrile as the co-solvent, acetonitrile as the first extractant wash and water as the second extractant wash for the intermediate cellulosic material are provided in Table 4. When acetonitrile is used as the co-solvent and first extractant wash 128, and water is used as second extractant wash 138, at least 90% or at least 95% of the cellulose in cellulosic material 103 is maintained in washed intermediate cellulosic material 136, as described herein. If no further processing is required, washed intermediate cellulosic material 136 may be referred to as finished cellulosic material, e.g., dissolving-grade pulp.

TABLE 4 WASHER 125 and WASHER 135 Conc. Conc. Conc. (wt. %) (wt. %) (wt. %) Washed Intermediate Cellulosic Material 126 Cellulose 25 to 88  29 to 83 33 to 78 Hemicellulose* 0.003 to 15    0.02 to 11  0.05 to 8.1  Extraction Wash 8 to 70 14 to 66 19 to 63 (Acetonitrile) Water 0 to 12  0 to 6.5 0.001 to 2.9  Used Extractant Wash 127 Water 0 to 16  0 to 8.3 0.001 to 3.9  Solvent (Ionic Liquid) 0 to 23 0.02 to 21  0.03 to 19  Co-solvent (Acetonitrile) 61 to 100  71 to 100  78 to 100 Washed Intermediate Cellulosic Material 136 Cellulose 25 to 88  29 to 83 33 to 78 Hemicellulose* 0.003 to 15    0.02 to 11  0.05 to 8.1  Acetonitrile 0 to 9  0 to 7 0.001 to 6    Water 11 to 70  13 to 67 15 to 63 Used Extractant Wash 137 Water  69 to 99.6  71 to 99.3  73 to 99.0 Solvent (Ionic Liquid)  0 to 7.7  0 to 7.0  0 to 6.5 Co-solvent (Acetonitrile) 0.4 to 24  0.7 to 23  1.0 to 21  *“Hemicellulose” in these designated streams includes hemicellulose, degraded cellulose and other impurities.

Used extractant washes 127 and 137 may be subjected to further separation (not shown) and reused within the process.

In some embodiments (not shown), washed intermediate cellulosic material 126 or 136 may then be further de-liquored, e.g., mechanically concentrated in a concentrator to form a concentrated cellulosic material having an increased solids content, e.g., from 10 to 99 wt. %, from 20 to 90 wt. % or from 30 to 85 wt. %. In some embodiments, the solids content is at least 90 wt. %. The concentrator may include squeeze rolls, rotating rolls, and/or ringer rolls as well as optional heat exchangers to vaporize the liquids. Additional water removal methods may be used to concentrate the cellulosic material, depending on the desired solids content and available energy supply. The concentrated cellulosic material may comprise from 2 to 99 wt. % cellulose (e.g., from 3 to 95 wt. % cellulose), from 1 to 60 wt. % water (e.g., from 1 to 50 wt. % water), and from 0.01 to 20 wt. % hemicellulose (e.g., from 0.5 to 10 wt. % hemicellulose). The concentrated cellulosic material may then be further dried in a dryer (not shown) as described herein.

In some embodiments, as described herein, when the process comprises more than one washing step, a concentrator may be utilized between washing steps or after all washing steps in order to improve washing efficiency for the cellulose solvent and co-solvent, as well as to maximize separation of any remaining hemicellulose, thereby reducing total washing agent quantity required and associated energy and disposal costs.

Depending on the purity of the starting cellulosic material, high purity α-cellulose product may be produced. In preferred embodiments, the finished cellulose product, e.g., dissolving-grade pulp, comprises high purity α-cellulose products such as high purity dissolving-grade pulps comprising at least 90 wt. % glucan, from 1.7 to 5 wt. % xylan, and less than 5 wt. % hemicellulose, e.g., less than 2 wt. % hemicellulose or less than 1 wt. % hemicellulose. In one embodiment, the cellulosic product has an UV absorbance of less than 2.0 at 277 nm, e.g., less than 1.6 at 277 nm, or less than 1.2 at 277 nm for hardwood species. Paper grade pulp typically has an UV absorbance of greater than 4.7 at 277 nm, as determined by standard UV absorbance measurements. Conveniently and accurately, purity of the α-cellulose product may be indicated by a lower absorbance at a certain wavelength.

In addition to retaining the fiber morphology of the cellulosic product, the dissolving-grade pulp also may advantageously retain other beneficial characteristics such as brightness. Further, the dissolving-grade pulp may have a weight-average molecular weight than the starting cellulosic material, e.g., at least 200% higher, at least 300% higher or at least 500% higher. The dissolving-grade pulp may be further processed to make cellulose derivatives, such as cellulose ether, cellulose esters, cellulose nitrate, other derivatives of cellulose, or regenerated cellulose fiber, such as viscose, lyocell, rayon, etc. Preferably, the dissolving-grade pulp may be used to make cellulose acetate.

Returning to extractant filtrate 109 or 111 as shown in FIGS. 1-3, the stream may be sent to a hemicellulose recovery unit 130 to form recovered extractant 131 and hemicellulose product 132. The recovered extractant 131 may contain cellulose solvent and co-solvent which can be recycled to extractor 105. Hemicellulose recovery unit 130 may comprise a filtration unit or an evaporator, a precipitator, distillation columns, washers, and dryers. The finished hemicellulose product, has a broad application to generate high value chemicals. Some, but not all, examples are described briefly here. Firstly, it may be advantageously used as an intermediate in ethanol, xylitol, furfural, methyl furfural, or valerolactone production. Secondly, the finished hemicellulose product may also be used as a feedstock to produce ethanol and/or as a fuel to a recovery boiler. Thirdly, hemicellulose can be used as a starting material to produce functional chemicals, such as adhesives and sweeteners. Fourthly, it can be recycled back to paper mill to make papers with special features.

While the above invention is applicable to processes in which mono-, di-, and oligo-saccharide and/or other side products may be generated in the extraction process, flashing process, and/or other operating steps, several other technologies can also be chosen to remove them from the system in order to maintain continuous operation. In some embodiments, evaporation, membrane, ion exchange, activated carbon bed, simulated moving bed chromatographic separation, flocculant, e.g. polydiallyldimethylammonium chloride (polyDADMAC), and/or their combinations may be employed to separate mono-, di-, and oligo-saccharide from the liquid stream. In other embodiments, polymer-bound boronic acid has been demonstrated to be able to form complex with sugars so that the sugars are separated from the liquid stream. In yet other embodiments, the small sugars may be converted by either enzymatic treatment or acid-catalytic process into furfural, ethanol, acetic acid, and/or other products which can be further separated out from the system. In still other embodiments, mono-, di-, and oligo-saccharide and other side products can be removed in one or more operations, which are located before the separation of the extraction filtrate, after precipitation step, in the hemicellulose wash steps, and/or in other steps. The operating conditions are also determined by the stability of the extractant. Without being bound by theory, this allows for the minimization of degradation products of the extractant. For a continuous operation, degradation products may be removed by directly purging a degradation products stream. Additionally, distillation may be used to purge degradation products from a column as a distillate or a residue, depending on the boiling point(s) of the degradation product(s). In some embodiments, combinations of these degradation product removal strategies may be employed.

Similarly, accumulated dissolved and/or suspended solids may be removed from the system in order to maintain continuous operation. In some embodiments, evaporation, membrane filtration, ion exchange, activated carbon bed, simulated moving bed chromatographic separation, flocculant, e.g. polydiallyldimethylammonium chloride (polyDADMAC), and/or their combinations may be employed to separate the accumulated dissolved and/or suspended solids from the system.

It is understood that the processes described herein may be further modified based upon the extraction capability, stability, and costs of ionic liquid and co-solvent.

The present invention will be better understood in view of the following non-limiting examples.

VI. Examples Example 1 Hardwood Pulp Single Extraction

A carbohydrate analysis and a gel permeation chromatography (GPC)/size exclusion chromatography (SEC) analysis of a dissolving-grade pulp prepared according to the present invention were conducted. The dissolving-grade pulp was prepared from a hardwood paper grade pulp (Comp. Ex. D in Table 5). The extractant composition comprised 3 wt. % EMIM Ac and 97 wt. % DMSO. The extraction was conducted at 95° C. for 1 hour with a pulp solid loading of 5 wt. %. After extraction, the pulp was deliquored with centrifugation and washed with fresh extractant (3 wt. % EMIM Ac and 97 wt. % DMSO), and then washed with water four times. After the water wash, the pulp was dispersed in water, and filtered with a Busch funnel under vacuum. The filter cake was washed one more time with acetone to remove additional water. Finally, the pulp cake was dried at room temperature in a chemical hood to a moisture content from 7 to 8 wt. % moisture content.

The carbohydrate analysis was conducted in the following manner. The samples were prepared according to TAPPI T249. Approximately 0.3 grams of pulp was prehydrolyzed in 3 mL of 72% H₂SO₄ at 30° C. for 1 hour, and then diluted to 4% H₂SO₄ concentration by adding water. The sample was autoclaved at 120° C. to completely hydrolyze the polysaccharides into monosaccharides. The hydrolyzed sample was then analyzed by Dionex ion chromatography with a pulsed amperometric detector (PAD). The results were calculated relative to sample weight on an oven-dried basis.

The SEC was conducted using three detectors in series: refractive index (RI), right angle and low angle light scattering (RALS/LALS), and four-capillary differential viscometer. The system was calibrated use a poly(methyl methacrylate) standard. The run conditions were as follows: a mobile phase contained 0.5% lithium chloride in N,N-dimethylacetamide (DMAC); the run was conducted at 60° C., with an injection volume of 100 μL and a flow rate of 0.70 mL/min using Viscotek I-MBLMW and MBHMW SEC/GPC columns.

The dissolving-grade pulp sample was prepared by placing approximately 0.05 g of the dissolving-grade pulp in 10 mL water at 40° C. to swell for 45 minutes. This was repeated. The sample was then washed twice with 8 m: methanol for 45 minutes at ambient temperature. 8 mL anhydrous DMAC was added twice consecutively at ambient temperature. The first wash of anhydrous DMAC was left for 45 minutes and the second wash was left overnight. The sample was then added to 5 mL of 8% dry LiCl/anhydrous DMAC, and stirred at ambient temperature for 48 hours for complete dissolution. The final dissolved sample was a clear viscous mixture of 8% LiCl/DMAC at a concentration of 10 mg/mL. The sample was then diluted to approximately 1 mg/mL before injection into the GPC instrumentation.

The UV measurement was conducted as follows. 1 mL of 72% sulfuric acid was added to 0.1 g of dry pulp. The mixture was incubated at 30° C. for 1 hour with stirring every 10 min. After incubation, the clear solution was diluted by 5 mL of deionized water. The UV absorbance at 277 nm of the diluted solution was measured. After hydrolysis by 72% sulfuric acid at 30° C. for 1 hour, the xylan in the pulp was converted into furfural which was measured by UV. Cellulose and mannose cannot be converted into 5-hydroxymethylfurfural (HMF) under these conditions. Therefore the UV purity is related to the xylan content in purified pulp. The higher the UV absorbance at 277 nm, the higher the xylan content in pulp. The pulp had a UV purity of 1 to 1.1, which approximately represents the xylan content in pulp to be 3 to 3.5 wt. %.

The results of the analysis are shown in Table 5.

Example 2 Hardwood Pulp Double Extraction

A carbohydrate analysis and a GPC/SEC analysis of a dissolving-grade pulp prepared according to the present invention were conducted as in Example 1. The dissolving-grade pulp was prepared as in Example 1, except that the pulp was subjected to a second extraction using the same extractant under the same extraction condition. The pulp had a UV purity of 0.7 to 0.8, corresponding to a xylan content from 1.2 to 1.7 wt. %. An elemental metal analysis was also conducted on the pulp of Example 2.

Example 3 Hardwood Pulp Double Extraction

The UV purity of a dissolving-grade pulp prepared according to the present invention was determined as in Example 1. The dissolving-grade pulp was prepared from a hardwood paper grade pulp (Comp. Ex. D in Table 5). The extractant composition comprised 3 wt. % EMIM Ac and 97 wt. % DMSO. The extraction was conducted at 95° C. for 1 hour with a pulp solid loading of 5 wt. %. After extraction, the pulp was de-liquored with centrifugation, and then the de-liquored wet pulp was returned to the extractor and fresh extractant was added (3 wt. % EMIM Ac and 97 wt. % DMSO). The extraction composition had a 5% pulp solid loading and the extraction was conducted for 1 hour at 95° C. After the second extraction, the pulp was washed and dried as in Example 1, except that there no fresh extractant wash was used before the water wash steps. Finally, the pulp cake was dried at room temperature in a chemical hood to a moisture content of approximately 7 to 8 wt. %. The purified pulp had a UV purity of 1.0 to 1.1, which represented an approximate xylan content from 3 to 3.5 wt. %

Comparative Example A Hardwood

A carbohydrate analysis and a GPC/SEC analysis of a commercial acetate grade pulp were conducted as in Example 1. The pulp was prepared from a hardwood according to a pH kraft process. The results of the analysis are shown in Table 5.

Comparative Example B Hardwood

A carbohydrate analysis and a GPC/SEC analysis of a commercial acetate grade pulp were conducted as in Example 1. The pulp was prepared from a hardwood according to a pH kraft process. The results of the analysis are shown in Table 5.

Comparative Example C Hardwood

A carbohydrate analysis and a GPC/SEC analysis of a hardwood pulp were conducted as in Example 1. The pulp was prepared from a hardwood according to a sulfite process. The results of the analysis are shown in Table 5.

Comparative Example D Hardwood

A carbohydrate analysis and a GPC/SEC analysis of a commercial paper grade pulp were conducted as in Example 1. The pulp was prepared from a hardwood and was the starting cellulosic material used in Examples 1-3. The results of the analysis are shown in Table 5.

TABLE 5 CARBOHYDRATE AND GPC/SEC ANALYSIS Comp. Comp. Comp. Comp. Example 1 Example 2 Example 3 Ex. A Ex. B Ex. C Ex. D Carbohydrate Analysis Arabinan (wt. %) <0.1 0.1 — <0.1 <0.1 N/A 0.2 Xylan (wt. %) 3.5 1.9 3 to 3.5 1.6 1.4 N/A 20.3 Mannan (wt. %) 1.2 1.1 — 0.3 0.6 N/A 1.0 Galactan (wt. %) <0.1 0.1 — <0.1 <0.1 N/A 0.2 Glucan (wt. %) 92.6 93.3 — 96.4 97.4 N/A 77.3 Acid Insoluble (wt. %) 0.7 0.4 — 0.2 0.7 N/A 0.6 Total (wt. %) 98 96.9 — 98.6 100 N/A 99.6 GPC/SEC Analysis Weight-Average 793,320 845,725 835,268 422,451 361,014 359.685 700,708 Molecular Weight (g/mol) Number-Average 273,901 269,540 178,361 76,651 149,729 88,577 143,951 Molecular Weight (g/mol) Z-Average Molecular 1,498,000 1,707,000 1,958,000 830.376 768,853 823,311 1,993,333 Weight (g/mol) Peak Molecular Weight 727,083 661,129 623,267 349,115 213,764 196,808 619,425 (g/mol) Polydispersity Index 2.90 3.12 4.68 5.51 2.42 4.06 4.79

Example 4 Elemental Analysis

The pulps of Examples 1-2 and of Comparative Examples A-B and D were subjected to elemental analysis. The metal scan analysis for these samples was determined by inductively coupled plasma-optical emission spectroscopy (IEP-OES). The results are shown in Table 6.

TABLE 6 ELEMENTAL ANALYSIS Elemental Comp. Comp. Comp. Analysis (ppm) Example 1 Example 2 Ex. A Ex. B Ex. D Al 1.3 1.8 1.1 1.1 2.8 As 0.5 <0.05 <0.5 <0.5 <0.5 Ba .69 0.53 0.27 0.42 4.03 B <0.2 <0.2 0.7 0.2 0.2 Cd <0.02 <0.02 0.02 <0.02 <0.02 Ca 204 164 15.8 20 279 Cr 0.41 0.49 0.08 0.05 0.11 Co 0.04 <0.02 0.02 <0.02 0.04 Cu 1.87 1.9 0.33 0.15 0.21 Fe 18.7 18.6 3.09 2.17 2.66 Pb 2.6 <0.2 <0.2 <0.2 0.2 Li 0.03 0.03 0.07 0.05 0.02 Mg 82.7 66.5 29.2 12.7 30 Mn 0.37 0.23 0.06 0.75 2.21 Hg <0.01 <0.01 <0.01 <0.01 <0.01 Mo 0.18 0.12 <0.05 <0.05 <0.05 Ni 0.64 0.44 0.15 0.14 0.17 P 0.8 0.7 0.6 0.6 0.6 K 2 2 8 2 12 Si 3.78 4.96 8.78 15.9 9.92 Na 13 12 217 289 729 Sr 0.57 0.46 0.15 0.24 1.61 Ti 0.26 0.41 0.22 0.16 0.37 V <0.05 <0.05 <0.05 <0.05 <0.05 Zn 11.1 10.9 1.68 0.80 1.81

Example 5

The pulps of Examples 1-2 and of Comparative Examples A-B and D were tested for carboxyl content, aldehyde content, copper number, and DCM extractives. The carboxyl content was analyzed per ESM 055B (ref: TAPPI T237, the entirety of which is hereby incorporated by reference); the aldehyde content was analyzed per ESM055B (ref: Rayonier Standard Procedure, the entirety of which is hereby incorporated by reference); the copper number was analyzed per ESM 071B (ref: TAPPI T430, the entirety of which is hereby incorporated by reference); and the DCM extractives were analyzed per ESM 077B (ref: PAPTAC G.13 & TAPPI T204, the entireties of which are hereby incorporated by reference). The results are shown in Table 7.

TABLE 7 PULP QUALITIES Comp. Comp. Comp. Example 1 Example 2 Ex. A Ex. B Ex. D Carboxyl 1.77 2.25 2.36 1.51 5.91 Content (meq/100 g) Aldehyde 0.22 <0.01 0.07 0.03 0.52 Content (meq/100 g) Copper 0.14 0.15 0.25 0.13 0.42 number Carbonyl 0.12 0.13 0.30 0.10 0.58 Content (meq/100 g) DCM <0.01 <0.01 0.03 0.02 0.13 Extractives

Example 6 Softwood Pulp Single Extraction

A carbohydrate analysis and a GPC/SEC analysis of a dissolving-grade pulp prepared according to the present invention were conducted as in Examples 1 and 5. The dissolving-grade pulp was prepared from paper grade softwood pulp. The extractant composition comprised 3 wt. % EMIM Ac and 97 wt. % DMSO. The extraction was conducted at 95° C. for 1 hour with a pulp solid loading of 5 wt. %. After extraction, the pulp was deliquored with centrifugation, washed with fresh extractant (3 wt. % EMIM Ac and 97 wt. % DMSO), and then washed with water four times. After the water wash, the pulp was dispersed in water and filtered with a Busch funnel under vacuum. The filter cake was washed one more time with acetone to remove water. Finally, the pulp cake was dried at room temperature in a chemical hood to a moisture content from 7 to 8 wt. %. The results of the analysis are shown in Table 8.

Example 7 Softwood Pulp Double Extraction

A carbohydrate analysis and a GPC/SEC analysis of a dissolving-grade pulp prepared according to the present invention were conducted as in Examples 1 and 5. The dissolving-grade pulp was prepared as in Example 2, except that a softwood pulp was used as a starting material. The results of the analysis are shown in Table 8.

Comparative Example E Softwood

A GPC/SEC analysis of a commercial acetate grade pulp was conducted as in Example 1. The pulp was prepared from a softwood according to a sulfite process. The results of the analysis are shown in Table 8.

Comparative Example F Softwood

A carbohydrate analysis and a GPC/SEC analysis of a commercial acetate grade pulp were conducted as in Example 1. The pulp was prepared from a softwood according to a sulfite process. The results of the analysis are shown in Table 8.

Comparative Example G Softwood

A carbohydrate analysis and a GPC/SEC analysis of a commercial acetate grade pulp were conducted as in Example 1. The pulp was prepared from a softwood according to a sulfite process. The results of the analysis are shown in Table 8.

Comparative Example H Softwood

A GPC/SEC analysis of a commercial acetate grade pulp was conducted as in Example 1. The pulp was prepared from a softwood according to a sulfite process. The results of the analysis are shown in Table 8.

Comparative Example I Softwood

A GPC/SEC analysis of a commercial acetate grade pulp was conducted as in Example 1. The pulp was prepared from a softwood according to a sulfite process. The results of the analysis are shown in Table 8.

Comparative Example J Softwood

A GPC/SEC analysis of a commercial acetate grade pulp was conducted as in Example 1. The pulp was prepared from a softwood according to a sulfite process. The results of the analysis are shown in Table 8.

Comparative Example K Softwood

A carbohydrate analysis and a GPC/SEC of a commercial paper grade pulp were conducted as in Examples 6 and 7. The pulp was prepared from a softwood according to a pH kraft process. The results of the analysis are shown in Table 8.

Comparative Example L Softwood

A carbohydrate analysis of a commercial paper grade pulp was conducted as in Examples 6 and 7. The results of the analysis are shown in Table 8.

TABLE 8 CARBOHYDRATE AND GPC/SEC ANALYSIS Comp. Comp. Comp. Example 6 Example 7 Ex. E Ex. F Ex. G Carbohydrate Analysis Arabinan (wt. %) 0.2 0.1 — <0.1 <0.1 Xylan (wt. %) 1.8 0.9 — 1.5 1.8 Mannan (wt. %) 5.6 4.9 — 1.1 1.1 Galactan (wt. %) 0.2 0.1 — <0.1 <0.1 Glucan (wt. %) 86.9 90.1 — 96.3 93.2 Acid Insoluble (wt. %) 0.1 <0.1 — 0.5 0.4 Total (wt. %) 94.7 96.1 — 98.7 96.5 GPC/SEC Analysis Weight-Average 2,368,500 N/A 671,393 638,516 500,753 Molecular Weight (g/mol) Number-Average 264,594 N/A 232,340 278,234 141,785 Molecular Weight (g/mol) Z-Average Molecular 26,860,000 N/A 1,256,000 1,127,000 953,861 Weight (g/mol) Peak Molecular Weight 305,714 N/A 589,350 589,350 396,680 (g/mol) Polydispersity Index 8.95 N/A 2.89 2.89 3.53 Comp. Comp. Comp. Comp. Comp. Ex. H Ex. I Ex. J Ex. K Ex. L Carbohydrate Analysis Arabinan (wt. %) — — — 0.5 0.6 Xylan (wt. %) — — — 8.9 9.5 Mannan (wt. %) — — — 7.0 6.4 Galactan (wt. %) — — — 0.3 0.2 Glucan (wt. %) — — — 76.5 79.6 Acid Insoluble (wt. %) — — — <0.1 <0.1 Total (wt. %) — — — 93.2 96.4 GPC/SEC Analysis Weight-Average 565,102 423,975 429,182 2,237,500 — Molecular Weight (g/mol) Number-Average 180,471 141,909 129,235 454,867 — Molecular Weight (g/mol) Z-Average Molecular 1,069,333 807,799 842,857 12,700,000 — Weight (g/mol) Peak Molecular Weight 510,524 364,948 306,513 546,395 — (g/mol) Polydispersity Index 3.13 2.99 3.32 4.92 —

Example 8 Silicon Content

The analysis of the silicon content for the pulps of Comparative Examples A-B, F-H and J was provided by atomic spectroscopy and is shown in Table 9.

TABLE 9 SILICON CONTENT Silicon Target Silicon Maximum (ppm) (ppm) Comp. Ex. A 7 23 Comp. Ex. B 19 47 Comp. Ex. F 5 14 Comp. Ex. G 12 37 Comp. Ex. H 12 28 Comp. Ex. J 12 37

While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. It should be understood that aspects of the invention and portions of various embodiments and various features recited above and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of ordinary skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention. 

We claim:
 1. A dissolving-grade pulp composition comprising at least 90 wt. % glucan and from 0.6 to 5 wt. % xylan, wherein the composition has a weight-average molecular weight of at least 500,000 g/mol.
 2. The composition of claim 1, wherein the composition comprises less than 175 ppm sodium.
 3. The composition of claim 1, wherein the composition comprises less than 25 ppm sodium.
 4. The composition of claim 1, wherein the dissolving-grade pulp is a hardwood dissolving-grade pulp.
 5. The composition of claim 1, wherein the dissolving-grade pulp is a softwood dissolving-grade pulp.
 6. The composition of claim 1, wherein the composition further comprises from 1 to 2 wt. % mannan.
 7. The composition of claim 1, wherein the composition comprises from 1.1 to 5 wt. % mannan.
 8. The composition of claim 1, wherein the composition further comprises arabinan and galactan.
 9. The composition of claim 1, wherein the composition has a weight-average molecular weight from 500,000 to 3,000,000 g/mol.
 10. The composition of claim 1, wherein the composition has a number-average molecular weight from 150,000 to 600,000 g/mol.
 11. The composition of claim 1, wherein the composition has a number-average molecular weight from 175,000 to 450,000 g/mol.
 12. The composition of claim 1, wherein the composition has a Z-average molecular weight from 900,000 to 50,000,000 g/mol.
 13. The composition of claim 1, wherein the composition comprises less than 7 ppm silicon.
 14. The composition of claim 1, wherein the composition comprises less than 10 ppm potassium.
 15. The composition of claim 1, wherein the composition comprises less than 0.01 wt. % dichloromethane extractables.
 16. The composition of claim 1, wherein the weight ratio of xylan to mannan is from 1:1 to 3:1.
 17. The composition of claim 1, wherein the weight ratio of xylan to mannan is less than 1:2.
 18. A dissolving-grade pulp composition comprising at least 90 wt. % glucan and from 0.6 to 5 wt. % xylan, wherein the composition comprises less than 175 ppm sodium.
 19. The composition of claim 18, wherein the composition comprises less than 25 ppm sodium.
 20. The composition of claim 18, wherein the weight ratio of xylan to mannan is from 1:1 to 3:1. 